Even as Aereo touched off an epic legal fight with broadcasters at the Supreme Court, it was unclear just how many people were paying to use the streaming TV service. This week, a potential clue emerged via a letter from the Copyright Office that cited Aereo’s submission of “royalty and filing fees totaling $5,310.74” for the period of January 1, 2012 until December 31, 2013.

The letter appeared on Thursday, and came in response to Aereo’s application to pay cable royalties under the Copyright Act’s statutory licensing rules.

The $5,310 number is significant because it represents a percentage of total revenue during the period for Aereo, which shut its service last month in response to a Supreme Court ruling. On Twitter, law professor Bruce Boyden suggested that the number reflected subscriber revenues of around $1 million for the period: